1. Field of the Invention
The invention relates to a valve mechanism, in particular for internal combustion engines of motor vehicles, with a driven cam element and with a valve actuator displaceable or pivotable by the cam element.
Valve mechanisms for the valve control of internal combustion engines, in particular for motor vehicles, conventionally have a device (spring, hydraulic element, etc.) by means of which the valve is acted upon in the closing position. At least during the open phase, therefore, the valve actuator (valve tappet, drag lever, rocker arm or the like) is pressed against part of the closed valve control surface, the part being eccentric to the shaft axis. During the closing of the valve, care must be taken to ensure that the valve disk does not strike the valve seat too quickly, since it otherwise rebounds. This requires relatively complicated coordination between the masses to be moved, the forces arising, the material properties, etc.
There has therefore been no lack of proposals for guiding the valve actuator positively on the cam element, various embodiments having been developed, which are each based on two eccentric valve control surfaces instead of the return spring.
Actual versions may be gathered, for example, from GB patent specification 19,193 (1913) and GB patent specification 434,247, wherein the cam element has, on at least one end face, a groove, the two side walls of which form the valve control surfaces. A roller or the like arranged at the end of the valve actuator engages into the groove from the side. A cam element having a surrounding web is known, for example, from European patent publication EP 429,277.
Further examples of positive guides make use, instead of valve control surfaces parallel to the axis of rotation of the camshaft, of two valve control surfaces which are arranged axially one behind the other and are formed on two differently shaped camshaft elements, for example European patent publications EP 355 659 B, and EP 384 361 A. etc.
Both the first version of the positive guides with end-face grooves and the lateral engagement of the sensing element and the second version with two earn elements and two sensing elements for each valve have, as compared with the first-mentioned valve mechanism with a return spring, an increased axial extent and a greater number of components which present either structural, spatial or economic problems.